Science in South Africa Special

25 November 2007

This week, we bring you the highlights of the Naked Scientists trip to South Africa. We explore what life is like in the poor regions of Johannesburg, and how the frightening reality of HIV and AIDS offers a silver lining in prevention research. Plus, In a journey through our evolutionary history, we come face to face with the two-and-a-half million year old Taung child, one of the most important human ancestor fossils ever found. Also, we find out why a moon like ours is rare in the universe, how opals get their colours and how mice choose a mate by smelling their wee. And in kitchen science, we learn how to throw your voice huge distances with the aid of a satellite dish.

In this episode

Research not so passive when it comes to smoke damage

Scientists in the US have produced strong evidence for the harmful effects of passive smoke inhalation.

Van GoghChengbo Wang and his colleagues at the children's hospital of Philadelphia made the discovery by using a new imaging technique called global helium-3 diffusion magnetic resonance imaging (MRI), to test the lungs of 60 volunteers aged between 41 and 79 years, including 15 current or former smokers and 45 lifelong non-smokers, half of whom had been exposed to high levels of passive smoking in the past (indicated by living with a smoker for more than 10 years). The subjects breathed in a small amount of a form of helium called helium-3, and the MRI scanner was used to monitor how the atoms moved around inside the subjects' airways, a measure called the ADC or apparent diffusion coefficient.

In healthy non-smokers the air spaces in the lungs are small and compact, which helps the blood to efficiently collect oxygen and shed carbon dioxide. This also means that the helium atoms don't tend to move very far.  But smoking causes lung tissue to break down, which is known as emphysematous change, and makes the air spaces larger.

When these changes are present the helium atoms can move much greater distances, and this can be picked up by the scanner. Indeed the researchers found that almost one third of the non-smokers with high exposure to secondhand smoke had structural changes in their lungs similar to the smokers, suggesting that damage was present.

"To our knowledge, this is the first imaging study to find lung damage in non-smokers heavily exposed to secondhand smoke," said Wang. "We hope our work strengthens the efforts of legislators and policymakers to limit public exposure to secondhand smoke.

Our moon could be rare

The moonOur moon is thought to have been created by a planet the size of Mars smashing into the proto-earth. The resulting debris is then thought to have formed the moon.  It is possible something similar happened to form Pluto's moon Charon.

Nadya Grolova and colleagues from the University of Florida has been looking for evidence of this sort of collision in other solar systems.  The technology to detect the planets directly doesn't exist but they are looking from the immense amounts of warm dust that such collisions would create, and the infra red radiation this dust would produce.  They have looked at 400 stars that are only only about 30 million years old, which is when most of these collisions are predicted to occur.  From their results they think that only 1 in 10-20 solar systems have these collisions and only some of the collisions will produce moons.

This is important because the moon is thought to have stabilised the orientation of the earth's axis thus making the earth's climate much more stable, and giving complex life enough time to develop.

"How mice "pee-ceive" who they're related to

Scientists have uncovered how mice identify their relatives and so choose not to mate with them - by the smell of their urine!

A house mousePrevious studies in mice and in humans, such as the smelly T-shirt test, had suggested that animals try to choose mates with a selection of immune system "MHC" genes that are as different as possible to their own.  But now Liverpool University's Janet Hurst and her colleagues have found that this is not true and instead mice rely on a diverse set of smelly chemicals in their urine called MUPs - major urinary proteins - which are encoded by the animal's DNA.  These give a mouse a chemical barcode, which it can compare against a potential mate.  If the smells match then the two animals are probably closely related, so they avoid mating with each other.  The scientists made the discovery by studying wild mice which were allowed to mate over several generations in a large outdoor enclosure.  After 15 weeks the researchers studied the parentage of the animals to work out which mice had mated.  They were surprised to find that the immune system genes previously believed to be the key to the process seemed to play no part whatsoever.

"Instead, another specialised set of proteins, which are produced at high concentration in mouse urine, signal relatedness through their scent.  It is these proteins that allow animals to avoid mating with their close kin," says Janet Hurst. The key to the breakthrough was the use in the study of wild as opposed to laboratory-bred mice.  Lab mice are all in-bred, so they carry the same urine proteins; as a result, researchers had focused instead on immune system genes.

Opals are thanks to Uranium

A Black OpalOpals are precious stones in which you can see vibrant colours which change as you move and look at them from different directions, in a similar way to how the colours you can see in a CD change and move as you look at them. The colour is produced by their structure not by pigments, opals are made of silica - the same thing as most sand, but it is in the form of billions of tiny spheres smaller than the wavelength of light.

Each sphere will reflect and scatter light from a slightly different place, all of these small reflections interfere with each other so in some directions for some colours they add together and in others they cancel each other out forming the beautiful colours.

Opals can be found in many types of rock and until now we didn't know what triggered them to form. Geologist Brian Senior and physicist Lewis Chatterton have studied opals very carefully using equipment such as electron microscopes and have discovered that the opal spheres seem to form in areas where silica is crystalising out of water. Normally this process cannot start in the centre of the water because there is nothing for the crystal to start to form on, so crystals grow out form the walls. But if there is Uranium decaying in the water the radiation it produces can from a nucleation point and start a crystal. All these small crystals form the centres of the spheres in the opal.

This is not just interesting science though because it means that opals are associated with radioactivity and so if you look for the radioactivity you may well find the opals.

Why do we huse helium an not hydrogen balloons?

In order to get a floating balloon you want a gas which is as light as possible. Helium is quite a lot lighter than air weight. It's about and eighth of the density of air. Hydrogen is about a sixteenth the density of air. So it'll float in air and will even float upwards. You'd have thought that hydrogen would be a better gas as it would give slightly more lift than helium because it's lighter. This is true. The problem is hydrogen is explosive and if you have children running around with balloons that could catch fire and blow up in their faces, it may have some health and safety implications. The other thing is that although hydrogen is half as heavy as helium it doesn't give you twice as much lift because the amount of lift you get is in its difference in density with [respect to] air. It's actually only another sixteenth of the density of air. It's a little bit better but not very much, so it's not worth the danger.

Helium is quite expensive, though, because it's a limited resource here on the planet. It's only created by radioactive decay on Earth. Atomic nucleuses emitting alpha particles that are actually helium nucleuses. They slow down and gain some electrons and turn into a helium atom. It tends to be found in oil wells where you get a gas-proof layer of rock above a load of rocks containing radioactive elements. They break down to helium. It floats up and gets trapped, often at the top of an oil well . The amount of helium that we can access cheaply is very limited because not all our oil wells have it.

Where are the bacteria on our bodies?

It is true, we are passengers in our own body. In fact, 10 is a conservative estimate. There are 50X more bacterial cells living in you and on you than there are cells in the rest of your body that are you.

Most of them are in the gut, of course, the intestines. We have them there because we have the perfect place for them to live. There's lots of things for them to eat; there's lots of gases which they can metabolise. Most of our insides are devoid of oxygen, for example, and lots of these bugs are anaerobes (they don't like oxygen). They do us a lot of favours and by having them there they're taking up resources and space which potentially nasty bacteria could take up. By having lots of these bugs in us they're in fact protecting us from being infected. When you go abroad and get diarrhoea what's actually happening is that the local bugs are combating your friendly bugs and beating them off for a while. Your body then learns to react and pushes the nasty ones back out so the friendly ones can re-colonise. Bacteria are roughly a tenth of the size, or smaller, than a human cell. In fact, if you look inside a human cell you can see evidence of evolution because there are these structures called mitochondria. Mitochondria are the cellular powerhouses. The mitochondria are the same size as a bacterium and scientists think they look so similar because way back in evolution a bacterium got inside an early cell. The two developed this partnership called the Symbiosis Theory and the bacterium lots of energy but the cell gave the bacterium protection and things it needed. The consequence was the two things lived happily side by side. But we're still living side-by-side with bacteria. We need them and if we don't have them in our guts then we're less healthy for the simple reason that if you rear animals and they're not allowed to have bacteria in their guts they don't do very well. This can mean that taking antibiotics may have negative effects. When you take antibiotics that are 'broad-spectrum' antibiotics these go through you like Domestos and kill the good bacteria. Anything that's left behind that's not vulnerable to the effect of antibiotic can then over grow. Yeasts and other fungi infections can do that because antibiotics won't kill those but they will kill the bacteria. Things like Clostridium difficiles, C. diff which leads to antibiotic associated diarrhoea and kills people in hospital. If people are but on heavy dose antibiotics then all the friendly bacteria get wiped out and these other ones over grow. It can be a big problem.

18:58 - Life in Soweto

We explored the township of Soweto, to discover what life is like for the poor in Johannesburg.

Life in Soweto
with Diran Onifade

South Africa is a country of contrasts - Johannesburg no less so. It's easy to see all the new cars, expensive houses, high-rise offices but just ten minutes south of the centre lies the township of Soweto where many people live in a shack. This is little more than a simple shed. To get an idea of what life is really like for the poor in Johannesburg, we spoke to one of the residents there.

Shack housing in Soweto, JohannesburgZareda - Hello my name is Zareda Shodwe and we are living in Soweto. We live in a shack, we don't have electricity or water yet. We have to go - maybe we pass five houses - to get water. We use gas stoves to cook and we light with candles in the house. We sometimes use the television and radio.

Chris - How many people live here?

Zareda - Five, six with my son.

Chris - Who are those people you live with?

Zareda - My sisters. One is older and three are younger than me.

Chris - What do you do for money? You're not able to go to work, you're looking after your son so how do you live?

Zareda - We sell vegetables. My older sister sells vegetables.

Chris - And are they vegetables you buy from someone else or do you grow them?

Zareda - We grow them, down there on the other side.

Chris - So tell us a bit about life for you here. What's it actually like to live here because this is pretty basic as a means of accommodation.

Zareda - Yes. When we live here people judge us for living here. When people pass the street they look at us in a different way. They don't think of us as people. They just think of us as people within the shack. It's not nice.

Chris - You've got a television here. You haven't got any electricity so how do you run your television?

Zareda - We use a car battery.

Chris - How long does that last?

Zareda - It lasts about six or seven days.

Chris - So television and radio must be quite important for you to get information.

Zareda - Yes it is important, it is important for us.

Chris - If you could change things here, what would be the most immediate thing that would make life better?

Zareda Shodwe speaking with Chris SmithZareda - Electricity. We don't mind not having houses but we just want electricity and running water in the house.

Chris - It's pretty draughty in here. There's holes in the roof.

Zareda - When it's hot outside the house becomes very, very hot. When it's cold the house is cold and when it rains it leaks.

Chris - What do you think is the prospects for your son? How will you make sure things go well for him?

Zareda - I don't know. If I can find a job I can make sure things go well for him.

Chris - Have you any plans of how you might make that happen?

Zareda - Yes, I do interviews. Sometimes I go for interviews but sometimes I don't get the job. Since I went for interviews I didn't get a job. I'm still sending CVs.

Chris - Were you born here?

Zareda - No, we were born in KwaZulu-Natal. My parents came here looking for a job.

Chris - And they brought you with them.

Zareda - Yes.

Chris - Do you wish in some respects they hadn't brought you here?

Zareda - No, I don't because in KwaZulu-Natal it is worse than here. The situation is worse than the one is here.

Chris - What do you think will be the situation in five years' time for you and your family?

Zareda - The government promises to change things so we hope things will have changed by then.

Chris - Now although five people and a baby living together in a corrugated metal shack not much bigger than my garage, with no electricity and no running water may sound very extreme to us. In many places the quality of life is a lot worse. Also with us in Soweto was Diran Onifade. He's a television journalist based in Nigeria. I asked him how the conditions we experienced compared with other parts of Africa.

Diran - To be honest with you, I will not describe these as very bad. I'm not measuring just by Nigeria but my fairly extensive knowledge of other African countries - because if you look at it they don't have electricity in their homes but there's still a situation where there is some illumination in the night.

Chris - Street lights and so on?

Diran - Street lights. And there is community water supply there for them 24 hours a day. They even have provisions for toilets. By African standards this is not how a squatter settlement is treated.

Chris - You're saying these people are fortunate?

Diran - In a way, yes.

Chris - It's hard to imagine worse though.

Diran - Well, you go to villages or even see who constitutes the urban poor in many African cities. It's far worse, much more people living in the same room without running water or food; toilets and, much the same way, without electricity. It's not good but it's not the worst that can happen on this continent.

Chris - How do you see places like this changing in the next five years? Do you think if we come back in five years' time we'll still be looking at the same sort of scene, a worse scene or will things have got markedly better?

Zareda Shodwe, Chris Smith and Diran OnifadeDiran - This is easy to change in the sense that they already have spaces well cut out for them. In many African cities people like them are thought of as squatters, to be flushed out. I think the most important things for them to have electricity, to work out for them to have some concrete structure. If that happens, I think their fortune is easy to turn around. Theirs is better than people who still live in mud huts with thatched roofs and things like that. There is no prospect of even getting electricity to them and there is no other pipe anywhere close by. I think it's easy to change their lot.

Chris - It's a bizarre environment because we drove in the car for ten minutes out of five star hotels, beautiful radio studios in the middle of Johannesburg and then we're here and it couldn't be more different.

Diran - It's what some analysts have been calling the five minute factor. Most cities, you see it in Nigeria; you see it in Ghana - wherever - most cities you just need to drive five minutes out of these cities and you'll see the flip-side of civilisation.

Ben - The trappings of cities were still actually there because when we were in that shack, Chris pointed out that she had a better DVD player than Chris has got at home.

How do electric toothbrush chargers work?

chrisIt does sound very strange, doesn't it?

They don't want to use actual contacts because in a wet environment like a bathroom the contacts will get dirty. They'll rust and they won't last very long. What they do is something else which is kinda cunning. Inside that little protuberance there's a coil of wire which connects to the mains. Basically you've got a current running backwards and forwards through that wire, and that produces a magnetic field. It's an electromagnet.

Inside the toothbrush is another coil going outside the protuberance, again, under the plastic going round and round then connecting to the toothbrush itself. If you have a changing magnetic field going near a conductor, the field will induce a current in that conductor. It's actually how a transformer works. The current inside the first coil makes a changing magnetic field and that makes a current flow inside the second coil without having to touch it. That charges the toothbrush itself.

This takes advantage of the fact that although electricity will not travel through the plastic, magnetism will...

28:13 - HIV and AIDS in South Africa

South Africa is officially the country with the world’s highest prevalence of HIV, with up to 50% of the population estimated to become infected. Chris met up with some of the researchers...

HIV and AIDS in South Africa
with Prof. Helen Rees, Dr Francois Venter & Dr Jocelyn Moyes, Witswatersrand University

The conditions we saw in
Soweto were a breeding ground for infectious diseases. Things like HIV and TB are no exception. This week the UN reduced its estimates for how many people are actually infected and affected by HIV. They also announced that South Africa is officially the country with the world's highest prevalence (in other words cases of the disease) anywhere.

There is one benefit to being a country with the most HIV and AIDS and also being relatively connected to the First World and that is that the scientists and doctors working there have some of the best statistics on disease that the world has to offer. I met up with some of those scientists working to try and understand this condition and to try and break the back of this epidemic.

Helen - My name is Helen Reese. I'm the executive director of the Reproductive Health and HIV Research Unit at the University of Witwatersrand, based in Johannesburg. The scale of the HIV epidemic is something that hasn't been known in the world ever before. We can say that 5 million people out of the 41 million people in South Africa are infected. What that really means is that 1 in 8 of every adult in this country are infected with HIV. It means that when we see pregnant women in clinics, between 1 in 3 and up to 1 in 2 are infected with HIV with a very high risk that they'll transmit the virus to their infant. In young girls aged between 15 and 24 about 1 in 4 of those young women are infected with HIV. If these were the statistics that we saw in a developing country a state of emergency would be declared.

Stylized rendering of a cross-section of the Human Immunodeficiency VirusChris - If you look at who those people are, is there any particular group- a subset of the population who are affected or is this everybody?

Helen - HIV can affect everybody and if you look in South Africa, indeed it affects all various groups. It affects rich and poor. However, if you look at the way that the epidemic is now spreading it is disproportionately affecting black South Africans and we do think that it's affecting young people much more than older people.

Chris - Do you have any ideas as to why it's affecting the people that it's affecting? Is it an educational thing? Is there something else going on?

Helen - I think there's a lot of something else that goes on. There's a whole mixture of issues here. There is the issue of poverty that as a background affects all infectious diseases. There is a historical issue that apartheid created the migrant labour system that's both destroyed the social structure of families but has also pulled men from their families and made them single male individuals living in urban settings where they take often second partners. There are other things as well. There are issues about other sexually transmitted infections and possibly just the virus that you've got and possibly receptivity of the population. It could be right down to basic science as an influencing factor as well and why we have such a bad epidemic.

If, indeed, there is some sort of scientific and basic biological explanation to this then we need to understand that if we're going to stand a change to make a vaccine.

Chris - Francois Venter - you work with Helen. What have we learned so far about how people actually pass this on and when they're most infectious and when, therefore, most of the transmissions occur?

Francois - It's only in the first few months that people harbour infections. They're still infectious after that but the scale of infectiousness is so much greater during those first few months. It's starting to explain some of the frustration as to why large scale provincial programmes in our country in particular but throughout southern Africa have not had the impact we'd hoped they would. Condom provision, for instance, in this country's actually very, very good. Education processes - if you measure it against people's understandings of HIV and the spellings of most, people understand what's going on. It hasn't changed the dynamics of the epidemic on the face of it.

Chris - Why are they still getting it then if they know all that?

Francois - I think what we haven't understood is when transmission actually occurs. It seems to be very concentrated in the first few months, immediately after infection. If you do not intervene in those first few months you actually lose the overall public health benefit of dealing with transmission.

Chris - So what you're saying is if everyone stopped having sex for three months, which is when you're most infectious when you first catch it then potentially, you could stop it in its tracks because people's infectivity falls so much after that period?

Francois - I guess you could probably break the back of the entire epidemic if you could just alter sexual behaviours for a very brief period of time.

Chris - What about drugs? That's the thing at the moment. It's the mainstay of how we're trying to deal with HIV. There's no vaccine so we've got to treat people that have got it rather than trying to prevent people getting it in the first place because, as we've shown it's part of the argument but not the whole solution. How do the drugs work and have you got access to them here in South Africa?

Francois - The drugs are very, very effective. They essentially switch off the manufacture of the virus and allow the body's immune system to regenerate. They are available in South Africa and have been relatively freely for the last 3 - 3½ years. In the rest of southern Africa it varies from country to country. Even in our own country from region to region. In some rural areas people battle to get access to these drugs. In urban areas access is relatively free and available.

Chris - We've heard about drugs and other behavioural education to try and cut this down. Jocelyn Moyes, you're working on another way to try and deal with this problem.

Jocelyn - It's an area that we're doing quite a lot of work in is vaginal microbicides. The two present products that are about to come the end of clinical trials will lock HIV from attaching to the body cells. They're a very large molecule which will sit on the HIV receptor of the cell and form almost like a key into the keyhole. When HIV comes along it can't get through the keyhole into the body's cells. The present microbicides we are testing come in a gel formulation which is applied vaginally to prevent HIV either attaching to the cells or replicating.

Chris - Just for women or can men get some benefit from this?

Jocelyn - Well, it's topically applied and controlled by a woman but there is a chance that there will be protection for the male partner as well.

Chris - Have you any feel for how effective this is? It's a lot to put your faith in. How do you know that you're going to get complete coverage or how do you know that you're going to get enough concentration to do away with the virus?

Jocelyn - We've got two candidates in phase 3 testing which is the efficacy testing - does it work or doesn't it work? We'll have one set of results early in next year and the other results probably early in 2010. So then I think we will have some proof of concept. Will it work or can't it work?

At the moment our basis is that these compounds are active against HIV in the lab. They've been active at preventing infection in animal models and they are safe to use in humans. That's our assumption to this point. Our efficacy in humans will be proved early next year and then again in 2010.

Chris - Just returning to you, briefly Helen. A lot of people are probably thinking, why should the rest of the world worry about what's happening in one other country? There are lots of problems in the world. Why should HIV in South Africa be such a big international issue?

Helen - It's not just HIV in South Africa. HIV globally is not going away. In fact in many countries it's re-emerging as a problem. The other thing that we know is with a disease that's as devastating as this that seeing life expectancy drop by ten year aliquots, almost year-on-year, that's going to have a profound impact on the social fabric in many African countries and on many other countries in the Far East that are affected. You must then think what that will do to the economies of those countries or what it will do to political stability and once again we are a global family. If we have instability and poverty and growing problems in one part of the world inevitably they will relate to what happens in other parts of the world. That's one argument. The other basic argument is the argument that I hope we never lose touch with is that we are one common human family and we cannot ever look at the level of suffering that we're seeing as an epidemic in this part of the world and just turn our back on it because it's not directly affecting us.

Chris - Pretty scary, aren't they, those statistics? One person in two who's pregnant, turning up at antenatal clinics and they're HIV positive. South Africa, the country as the UN's put it, 'with the world's worst prevalence of HIV.'

37:13 - Our Story: Human Ancestor Fossils

One of the fantastic opportunities we had in South Africa was to visit the collection of fossils at Witwatersrand University. They have a collection of about 30% of the fossils found in...

Our Story: Human Ancestor Fossils
with Professor Lee Burger, University of Witwatersrand

One of the fantastic opportunities we had in South Africa was to visit the collection of fossils at Witwatersrand University. They have a collection of about 30% of the fossils found in Africa that tell us about how we evolved from ape-like creatures into modern humans.  Professor Lee Burger comparing FemursProfessor Lee Berger took us though some of the highlights of the collection, piecing together three million years of evolution in the process.  One of the most interesting things that the fossil record reveals is that we went through a period of extreme giantism. These were people routinely over 7ft tall, they were huge.  This was before we turned into the modern humans of today.

Lee - You've probably heard the myth that ancient humans were tiny and some of them were tiny.  But, as we moved through the period of 0.5 million to 300,000 years ago in Africa we move into the sort of mystery period where there's just a tiny handful of fossils.  The ones we find from that part are incredibly intriguing.  By this time you're going to begin seeing Neanderthals in Europe.  Inside of Africa they go through one of the most incredible things that we've only just begun to realise.  They go through a period of giantism.  What I'm pulling out of this bag may shock you!

Chris - Oooh!

Lee - Hahaha.

Chris - What we're looking at is the most enormous femur: the bit that forms your hip joint. That's huge.  As a doctor I know how big they normally are, that's huge.

Lee - They are huge.  That's so big we can't even calculate how big this individual was. You would need an NBA basketball player to get someone of the height someone like this would have been.  Something like over 7 feet tall.

Chris - You don't think this one's just an abnormality?

The fossilised brain of the Taung ChildLee - No because we found a lot of them.  Everywhere we find them we find them enormous.  These are what we call archaic Homo sapiens.  Some people refer to them as Homo heidelbergensis.  These individuals are extraordinary, they are giants.

Chris - Does it coincide with a time when there was enormous amounts of resources, lots of food which meant they could afford a huge body size like that?

Lee - Actually it might have been just the opposite.  That is, it was a period when there were larger amounts of grassland evolving and there were lots of giants adapting to that grassland.  Giant buffalo with horns three metres across if you can imagine that.  These individuals in that very rugged environment, that tough environment, seemingly were using their body size to enforce themselves into what was a very dry and tough period.

Chris - So when would he have been around?

Lee - This particular individual existed probably about 350,000-400,000 years ago.

Chris - How long did people with this giant stature exist for before they started to shrink again?

Lee - We have no idea but we do know that the next time we start getting a good window in is 100-150,000 years ago when we're here.  People of our stature, our body size.  This experiment was relatively short-lived (a couple of hundred thousand years).

The face of the Taung ChildChris - So that was all happening about 300,000 years ago but what about if we wind the clock back now to almost the very beginning?  To the earliest human ancestors who walked around on two legs.  These were the Australopithecines and they emerged about 3 million years ago.  The first ever example was unearthed by the famous palaeoanthropologist, Raymond Dart.  In the early 1920s he was working with his students in the Taung limestone works which is in the Harts Valley in the Bechaunaland, South Africa.  There, he discovered what turned out to be one of the most important fossils of all time.

Lee - This little brown box I'm opening up is the actual box Raymond Dart had built, back in 1925 to hold, arguably, the most important single human ancestor fossil on the planet.  You're about to join a really exclusive club of people who've actually seen and touched it.  This is the one that defines what it is to be an early African ape-man.

Chris - This is 3 million years old?

Lee -   This is about 2 ½ million years old.  We've actually largely dated it by comparing it to other fossils that have been found since.  It is an awe inspiring fossil but, remarkably still, the only fossil that was ever found at the Taung site.  It just happened to be this little child which is the first fossil of an early human found in Africa.  This started the entire science.  In fact, you can even argue that things like genetics and the study of our own origins came out with this fossil.  Discovered in the Taung lime quarry, it was sent in a box full of baboons to Raymond Dart and if it had arrived on almost anyone else's desk at that particular time they might not have recognised it.  What he pulled out of that box, the first thing he saw - if I pull out this little plastic bag - is that remarkable little thing:  half an endocast of a brain of a little child.  Immediately, Raymond Dart recognised that he wasn't holding a baboon brain in his hand.  It wasn't even a brain of a chimpanzee.  It was far too big. He was holding something that no one had ever seen before.  He probably would have used the term, 'a missing link.'

Chris - That's totally extraordinary.  How does something so soft and blancmange-y as a brain actually get preserved?

Lee - Well, because it doesn't.  That's not actually the brain.  What that is, is a cast of the interior of the skull.  very time your heart beats, as your head is forming as a child, it beats am impression of the surface of the brain onto effectively the inside of your skull.  The Taung ChildWhen a skull is up in these remarkable fossilisation situations there's a perfect impression - a perfect image of your brain on the inside of that skull. When it fills with fine sediments we then have a perfect cast of the brain.

Chris - You can literally, looking at that from the side, see the three major parts of the brain.  I can see what's going to be the cerebellum, the hind brain at the back, there's the temporal lobe - which is us is adjacent to our ear and then the frontal lobes where I'd be thinking and planning - I don't know whether this would have done much thinking and planning.  That's an incredible fossil.

Lee - It is one of the most remarkable fossils in of itself, that you'll ever see.  Look at the veins on the surface!  The blood supply to the brain is actually preserved on the surface of that.  Raymond Dart turned this little thing over just like I'm doing right now and looked down and saw this was not a rearward facing point of attachment facing this skull in the spinal cord.  It was vertically positioned.

Chris - That says it was not ape-like.  That's homo.

Lee - 'I walk on two legs,' that's what it spoke to him as clearly as if it were written on the fossil itself.  If that had been all he found it would have been fantastic but it wasn't all he found.  Inside of another block he saw this little mushroom-shaped attachment and in it he saw the back of a mushroom-shaped ...

Chris - Oh my god!

Lee - Yes, oh my god!

Chris - I've just got a glimpse of what's going to come out of this bag.

Lee - He took his wife's knitting needles and started chipping away at it.  On December the 21st, 1924 that rock broke away and he saw that.

Chris - It's a face.  I'm looking at a face.  It's phenomenal.

Lee - You're looking at maybe the most famous face in all of palaeontology.

Chris - It's perfect.

Lee - It's absolutely perfect because it doesn't have just the top, it has the bottom.

Chris - It's got a jaw and a face to go with it.  It's still quite monkey-like though isn't it?

Lee Berger and Chris SmithLee - A little bit.  It doesn't have quite the prognathism that a young monkey would have and what it certainly doesn't have is a big canine.  We're going back to something that's transitional.  It's a bit of the way between us and them.  It's our link.  This little child met a tragic, tragic end and about 3 ½ years of age.  I'll do something for you.  I'll put it all together, the whole Taung child.  Reunited, after being  2 ½ million years underground.

Chris - I think that probably is the most awe-inspiring experience, or one of them, I've ever had.

Lee - It is, it's about our experience.  Do you want to touch it?

Chris - Go on then.  So if I touch this, how many other people will have had the opportunity apart from Raymond Dart to have done that?

Lee - No more than a few hundred scientists and a few dozen people who aren't scientists.

Chris - That is absolutely incredible.  To say I'm blown away would be an understatement actually.  It's when I saw the face staring out at me through that plastic bag, it's almost moving me to tears.  It's just so incredible and delicate and perfect.

Lee - Yep, and 2 ½ million years old.  And it's our story.

Ben - The emotions were running quite high in that room and it was an honour to see that skull.  But if you're wondering what happened to that child, it was actually snatched away and killed by an eagle.  The fossilised bones of the skull have preserved the scratches from the bird's talons.  They compared it to baboons and they could see that that's what it was.  That was Professor Lee Berger showing us some of the most important human ancestor fossils ever found.

Why can't I see my watch when wearing sunglasses?

Ryan is probably wearing what's called polarised sunglasses. What they do is they only let one polarisation of light through. Light is a wave and can be thought of as a bit like a piece of string. So if I had a piece of string between me and you there I could probably loosen it by wobbling it up and down and that would make the waves move vertically. I would call that vertically-polarised light. Or I can make waves by wobbling it horizontally and that would be called horizontally polarised light.Light can be either of these, or any other polarisation in between. In fact, light coming from a normal light bulb or a fluorescent tube or the sun has all of them mixed together. Every possible polarisation.Then you get things called polaroids which your sunglasses are. These will only let one polarisation through. If you have them horizontally it will only let horizontal through or vertical will only let vertical through. If you've got two of them, if they're both horizontal light can get through it because light can get through the first one and the second one. If you rotate the second one to vertical nothing will get through because the first one stops horizontal and the second one stops vertical. LCD's use this because they have polarisers on them. Light comes though from underneath and gets polarised so only the vertical is coming through. Then you have something called Liquid Crystals which can twist the polarisation of light by 90 degrees: they are set up so light can get through normally. But if you then apply an electric field to it, the crystals stop twisting the polarisation so no light will get through and it'll go black. This means the light coming out of the LCD (Liquid Crystal Display) is polarised in only one polarisation so if your sunglasses are orientated in the right way it can block it and it'll go blank.

49:31 - Strange patterns with Sunglasses?

Why do polarising lenses cause you to see strange patterns in glass and metal?

Strange patterns with Sunglasses?

John Parker, Dept Engineering & Materials at Sheffield University:The question we've been asked concerns why you see strange patterns on glass when you look at it with polarised light (light that only vibrates at one angle - see this question) and the answer to that really comes in the fact that the glasses that have been looked at have been toughened by thermal quenching - by cooling very rapidly. The consequence of doing that is that you get stresses in the glass which have a different orientation according to where the cooling nozzles were in the original system used for quenching. So in some parts of the glass the stresses are running up and down, in some parts they're running across and so on. The light, as it travels through the glass interacts with those tresses differently and in effect you end yup with two rays travelling through the glass in different polarisation senses, travelling at slightly different velocities. When they emerge, the recombine and they're a bit out of step. What you're eye is seeing is a colour associated with just how out of step they were. That's the explanation for the effects you see with toughened glass.With metals, the answers almost certainly to do with the fact that when you get a reflection from the metal surface you some get some polarisation. You may, possibly have, an oxide layer which is as a result of tarnishing and things. All of these effects influence polarised light as it comes though.

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